Current Events Discussion

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chriwi
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Re: Current Events Discussion

Post by chriwi » Thu Apr 08, 2010 5:46 am

Interesting to see that during the last run (try to Squeeze) most of the energy of both beams waslost successively in the ring (probablyeaten by the collimators) and onlya small portin ended up in the dump finally.
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Re: Current Events Discussion

Post by Kasuha » Thu Apr 08, 2010 7:39 am

Beam losses are logical during such operations. They are trying to find optimal settings ... which involves going through some which are not optimal, too.

And as far as I know, Squeeze means focusing the beam to collision point which means it will become defocused behind it. That must be stopped by another set of focusing magnets behind the IP. Setting this wrong just a little bit means the beam defocuses along its path and generates losses. They did pretty good job IMO if the losses were so small.

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Re: Current Events Discussion

Post by chriwi » Thu Apr 08, 2010 8:16 am

Hi Kasuha,

I also agree that beam reduction is a usual thing while playing withvthe tuning and focusing. My point was only that it surprised me that they could deposite larger portions of the beam energy into the mashine without using the dump and also without causing anydamage. Ofcorse have to take in account that the total beam energies are far below the maximum power the LHC was desingned for.
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Re: Current Events Discussion

Post by oxodoes » Thu Apr 08, 2010 8:20 am

The collimators are designed to gradually absorb the nominal beam energy (nearly 3000 bunches per beam at 7 TeV) in the case of a dump malfunction.

Edit: I came to this conclusion after reading this page: http://www.lhc-facts.ch/index.php?page=kollimator (in German), the LHC collimator page sadly isn't very useful.
Last edited by oxodoes on Thu Apr 08, 2010 9:26 am, edited 1 time in total.

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Re: Current Events Discussion

Post by chriwi » Thu Apr 08, 2010 8:24 am

Thanks, this was my topic, evenso I did not know this statement before.
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Re: Current Events Discussion

Post by DCWhitworth » Thu Apr 08, 2010 9:46 am

They are currently running using a 'setup beam' which I believe is defined as a beam that is sufficiently low in intensity that it will not damage the machine should something go wrong.
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Re: Current Events Discussion

Post by Kasuha » Thu Apr 08, 2010 11:15 am

oxodoes wrote:The collimators are designed to gradually absorb the nominal beam energy (nearly 3000 bunches per beam at 7 TeV) in the case of a dump malfunction.

Edit: I came to this conclusion after reading this page: http://www.lhc-facts.ch/index.php?page=kollimator (in German), the LHC collimator page sadly isn't very useful.
Design report does not mention this gradual absorbtion but it states that a collimator should be able to withstand direct hit from entire SPS inject batch (72 bunches) at ultimate intensity and 450 GeV - or at least 8 bunches at ultimate intensity and energy (7 TeV).
What they were playing with was just one bunch at greatly reduced intensity, even if it was steered off the beam pipe there's good chance it wouldn't do any substantial damage.
What was probably happening was just that the beam became defocused and scraped by collimators, that's way below what they are built for.

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Re: Current Events Discussion

Post by oxodoes » Thu Apr 08, 2010 11:31 am

Ok. So what about the following scenario: The LHC is filled to its design specification (2808 bunches at 7TeV) and now a kicker magnet experiences a malfunction (not just an asynchronous dump, but the magnet is not available at all, we have seen this happening for example in the SPS). Will the collimators be able to still protect the machine and do they have to be renewed afterwards??

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Re: Current Events Discussion

Post by Kasuha » Thu Apr 08, 2010 11:53 am

I don't really see how this can happen taking the dump system design into account. But anyway - collimators are designed to (among others) clean up the abort gap so they probably can wipe the whole beam with them if necessary. I didn't say they can't do that, I only said design document does not mention it.

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Re: Current Events Discussion

Post by Danny252 » Sat Apr 10, 2010 1:08 am

Seems like they've managed a successful test with a 1E11 bunch! Kinda makes the current 5E9 bunches seem inadequate ;)

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Re: Current Events Discussion

Post by Kasuha » Mon Apr 12, 2010 7:54 am

I wonder what happened in the morning, both beams and energy went straight down all at once, doesn't look like standard procedure.

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Re: Current Events Discussion

Post by pixelmasseuse » Mon Apr 12, 2010 12:35 pm

Kasuha wrote:I wonder what happened in the morning, both beams and energy went straight down all at once, doesn't look like standard procedure.
cryo loss in one of the sectors...

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Re: Current Events Discussion

Post by NormReitzel » Mon Apr 12, 2010 1:01 pm

That, my friends, looks a whole lot like a quench. Since they're back up this morning, clearly it was not, or QPS did it's thing properly. I'd like to know if they had time to dump beams properly before the field collapsed, and what the time scale on the field loss actually was.

Where do they dump all that magnet energy on such a short time scale?

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Re: Current Events Discussion

Post by chriwi » Mon Apr 12, 2010 1:08 pm

That was only the same kind of drop as many times before, the only difference this time was that since Sector 56 was affected the current of the magnet shown on the vistar also dropped and was displayed right away, befor only ohter sectores droped and displayd was onloy the rampdown of then ot droped sectors (especially sector56). So, nothing new onlya new view of an old story.
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Re: Current Events Discussion

Post by jmayes » Tue Apr 13, 2010 3:24 am

From P1: "Stable beams (at last)...., squeeze tomorrow after 8:30 meeting"

If I am reading this right, they hope to hold stable beams for about 3 hours (5:20 now), then try the squeeze. I wish them luck! 8-)

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